Catheter steerable by directional jets with remotely controlled closures

ABSTRACT

A catheter is provided with a directional steering capability by one or more jets ejecting fluid from the distal end of the catheter in a radial direction which causes the catheter tip to bend in the opposite direction by reaction force. Actuation of the jet is controlled by a closure valve at the jet orifice, the closure valve being driven by a signal transmitted from the proximal end of the catheter. Preferred signals are either fluid pressure signals or electrical signals.

This invention lies in the field of medical catheters and relates inparticular to means for steering catheters to direct their distal tipsinto branched or convoluted bodily passages.

BACKGROUND OF THE INVENTION

Catheters are widely used in medical procedures, since they provideaccess to internal bodily passages and cavities for both diagnostic andtherapeutic purposes without surgery. Catheters have proved valuableover the years for use in regions of the body such as the heart andcoronary arteries, the brain, and the genito-urinary tract.

A critical procedure associated with the use of medical catheters is theinsertion of the catheter into the body and the placement of thecatheter tip at the appropriate location. Precise placement of thecatheter tip is often critical to the success of the function thecatheter is intended to perform, since the function must often bedirected to a highly localized region of internal tissue while avoidingareas which are immediately adjacent. In addition, bodily passages areoften of a very small diameter, and the interior wall of the passage isoften delicate and susceptible to puncture. Steering capability isimportant, for example, in cardiovascular surgery when catheters areused as an alternative to bypass surgery to selectively remove plaquefrom arteries. The use of a catheter in these procedures offerssignificant benefits in terms of lower cost and lower risk. Steeringcapability is of particular importance in procedures involvingperipheral arteries where plaque or thrombi are to be removed. Inobstetrics and gynecology, catheters can be used in conjunction withdilatation and curettage procedures for the selective removal ofexcessive tissue and cyst growth, and directional control is importanthere as well. The same is true for the use of catheters for the deliveryof site-specific treatments for ovarian cancer. Directional control isalso important in urology procedures involving catheters. Examples ofsuch procedures are the selective removal of prostate cancer and thetreatment of urinary tract blockages infections. In certain oncologyprocedures, accurately guided catheters can be used for the selectiveremoval of malignant tissue without affecting critical healthy tissuelocated nearby, and for improved biopsy methods, where it is importantto reduce the incidence of trauma in healthy tissue. In neurosurgery,catheters can be used for the removal of intracranial hematomas andsimilar procedures, and precise directional control of the catheters iscritical. In radiology, close directional control provides imaging andmapping catheters with active stabilization within the cardiac chamber.In internal body procedures in general, guided catheters are useful forsuch procedures as fluid aspiration to relieve abscesses and localizeddrug delivery. Other procedures and applications where steeringcapability is important will be readily apparent to the experiencedmedical practitioner.

Steering mechanisms have been devised for directing the distal tip ofthe catheter in a desired direction by remote control from the proximalend. One such mechanism includes a series of wires running the length ofthe catheter body on either side of its central axis and terminating inshims or thin strips at the distal end of the catheter. The operatorsteers the catheter by applying tension to one shim relative to theother, thereby causing the distal end to curve in the direction of thewire to which tension has been applied. The wires and the mechanism atthe proximal end for selectively applying tension are unwieldy, however,and susceptible to breakage. Furthermore, they offer limited directionalchoice without twisting the entire catheter to achieve angularadjustments relative to the catheter axis.

Guidewires are widely used to assist in the placement of catheters inlocations which are particularly difficult to reach. A guidewire istypically of very narrow diameter to fit within the lumen of a catheter.This permits the operator to slide the catheter over the guidewire afterfirst directing the guidewire to the appropriate location. It alsopermits the operator to remove one catheter and replace it with anotherwithout removing the guidewire and hence without the cumbersomeprocedure of independently relocating the catheter tip to the region ofinterest. The steering of a guidewire is generally accomplished byconstructing the guidewire to include a slight curvature at its distaltip, the tip being resilient in construction to resume the curvaturewhen relaxed. This enables the operator to direct the guidewire tiplaterally into branches of the vessel. To do this, however, the operatormust rotate the guidewire from the proximal end so that the tip curvesin the desired direction.

SUMMARY OF THE INVENTION

The present invention resides in a catheter with a steering capabilitywhich significantly reduces or eliminates the difficulties enumeratedabove, as well as other difficulties associated with catheter steeringmechanisms of the prior art. Steering is accomplished by one or morejets of fluid at the catheter tip, directed radially outward and causingthe catheter tip to move in an opposite direction due to the reactionforce. Preferably, a plurality of jets are included, formed by a seriesof ports distributed around the circumference of the catheter. Thebending of the catheter tip in any particular direction is achieved byselecting a jet to emerge from the opposing side of the catheter to theexclusion of the remaining jets. Further directional control can beachieved by using two or more adjacent jets so that the reaction forceis opposite to the combined vector of the jets.

Fluid is supplied to all of the jets through a single lumen whichextends the full distance to the catheter's distal end to communicatedirectly with each of the ports. The ports are individually andindependently opened and closed by closures which are operated bysignals transmitted from the proximal end of the catheter. The signalsto operate the closures is transmitted to each closure independently ofthe remaining closures. The signals may be any of various types, the twomost prominent being pressure signals and electrical signals. Closuresactuated by pressure signals include pivoting closures and slidingclosures, where pressure differentials govern the position of the pivotor of the sliding member. The same types of closures, and particularlysliding closures, may be actuated by electrical signals, by meansanalogous to electrically operated valves.

For embodiments in which the closures are operated by pressure signals,fluid pressure is transmitted to each closure independently of theremaining closures and of the fluid to the lumen supplying the jetsthemselves. In some of the preferred embodiments of the invention, theclosures are operated by levers, and the fluid pressure which driveseach closure imposes a pressure differential across the lever. Theopening and closing of the closure is thus controlled by the impositionand direction of the pressure differential. The levers are part of theclosure structure and are likewise located at the distal end of thecatheter. Independent transmission of fluid pressure to each lever isachieved by individual lumens traveling the length of the catheter, eachof these lumens being independent of the lumen supplying the jets. Todistinguish among the various lumens, the term "primary lumen" is usedin this specification to refer to the lumen supplying the jets, whilethe term "secondary lumens" is used to refer to the lumens supplying thefluid pressure which controls the closures.

The actuation of any single jet, and the selection among the variousdirectional jets when a plurality of jets is present, is thus achievedby closures positioned at the sites of the jets themselves, i.e. , atthe distal end of the catheter, while the operation of these closures isachieved by remote control from the proximal end of the catheter. Thisoffers a number of advantages to the operation and effectiveness of thedirectional control. For example, closures arranged and operating inthis manner permit a quick response to signals from the proximal end ofthe catheter for changes of direction. Furthermore, the use of a singlelumen supplying all of the jets rather than a series of lumens to supplyeach jet. individually permits one to use a jet supply lumen of a largerdiameter without increasing the outer diameter of the catheter. With alarger diameter lumen, any frictional loss of jet fluid as the fluidflows the length of the catheter is substantially reduced. Stillfurther, the control of the closures through secondary lumens which areseparate from the primary lumen used for the jet supply permits theclosures to be operated by pneumatic pressure, which can be transmittedmore quickly and modulated with a faster response than liquid pressureas is preferably used in the jets themselves.

In embodiments of the invention that entail the use of pneumatic orother fluid pressure to actuate the closures, the supply of the fluidpressure to the individual closures on a selective basis is achieved bya series of valves which are operatively connected to the secondarylumens at the proximal end the catheter. The valves are individuallycontrolled in any of a variety of ways known to those skilled in theart, and their selection may be conveniently governed by a manually orelectronically operated directional selector.

The term "fluid" is used herein to include both gases and liquids. Oneor the other will be preferred in specific applications, depending onthe region of the body into which the catheter is to be directed.

The term "catheter" is used herein to include both functional cathetersand guidewires. The invention thus extends to guidewires whose solepurpose is to be directed to a particular situs in a bodily vessel andonce at that situs to serve as a guide for insertion of a functionalcatheter to the same situs. The invention likewise extends to functionalcatheters themselves which may be used without a separate guidewire, thefunctional catheters containing any of a variety of functional elementsfor either diagnostic or therapeutic purposes. The catheters of thisinvention may thus contain additional lumens serving functions unrelatedto the directional jets, or additional transmitting elements fortransmitting signals such as optical or electronic signals from thedistal end of the catheter to the proximal end, or both lumens andtransmitting elements.

Additional features and advantages of the invention will be apparentfrom the description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view in perspective of the distal end of oneexample of a catheter constructed in accordance with the presentinvention.

FIG. 2 is a planar view of an angular segment of one portion of thecatheter depicted in FIG. 1.

FIG. 3 is a perspective view of the distal end of a second example of acatheter constructed in accordance with the present invention.

FIG. 4 is a perspective view of the distal end of a third example of acatheter constructed in accordance with the present invention.

FIG. 5 is a planar view of an angular segment of a fourth example of acatheter within the scope of the invention.

FIG. 6 is a side cutaway view of the catheter of FIG. 6.

FIG. 7 is an exploded view in perspective of a fifth example within thescope of the invention.

FIG. 8 is a combination block diagram and schematic drawing of a systemincorporating a catheter in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

While the invention is broad in scope and defined as indicated above bycertain parameters each of which entails a range of variations, theinvention is best understood by detailed descriptions of specificexamples. Five such examples are shown in the drawings.

The first example is depicted in FIGS. 1 and 2. FIG. 1 shows the distalend of the catheter in this example is shown in disassembled andexploded form. The catheter body is formed in three parts--an elongateshaft 11 which comprises the bulk of the catheter, a ring 12 which abutsthe elongate shaft at the distal end of the shaft, and a sleeve 13 whichencircles both the end of the shaft 11 and the ring 12, securing thering to the shaft. Construction of the catheter in three parts promotesease of manufacture, and permits a high degree of precision in theformation of the lumens, ports and closures, as discussed below, on aminiature scale.

The distal end 14 of the shaft 11 shows the arrangement of the lumens,each of which extends the full length of the shaft. The primary lumen 15is coaxial with the shaft, i.e., it shares a common central axis withthe shaft. The primary lumen 15 has the largest cross-sectional area ofall lumens in the shaft. The secondary lumens 16 in this example arefour in number, distributed around the periphery of the primary lumenand equally spaced. Each of these secondary lumens is of considerablysmaller cross-sectional area than the primary lumen.

The cross-sectional geometries of the lumens are not critical and mayvary. The primary lumen preferably has a circular cross section forpurposes of maximizing the ratio of cross section to perimeter lengthand thereby minimizing the shear force on fluid passing through thelumen. This will minimize the pressure loss of the fluid along thelength of the catheter, since the fluid will typically be a liquid suchas saline. The secondary lumens will function effectively with aflattened or oblong cross section, which will permit them to transmitpressure adequately while still leaving a large segment of the cathetercross section for the primary lumen. Since the pressure transmissionfluid in the secondary lumens remains substantially static regardless ofthe pressure, there is less of a concern in regard to fluid friction andpressure loss than in the primary lumen.

The number of secondary lumens and their arrangement around the primarylumen, and consequently the number and arrangement of jets at the distalend of the catheter, as described below, may vary. The catheter willfunction in accordance with the invention with as few as one secondarylumen and associated jet. Such a jet would produce a reaction force inone direction only. Changes of direction are then accomplished byrotating the catheter from its proximal end. In most applications,however, best results will be obtained with a total of 3 to 12 secondarylumens and associated jets, spaced at substantially regular intervals.In preferred constructions, the lumens and jets will number from 4 to 8.The lumens may be spaced apart from each other at regular intervals, orcombined in pairs which are spaced apart at regular intervals, or othersimilar arrangements. The arrangement, in any event, will be one whichpermits a selection of any single jet or pair of adjacent jets toproduce a reaction force in any desired direction without rotation ofthe catheter.

The ring 12 contains the lateral apertures which form the jets, as wellas the closures which open and close the jets. These elements and theiroperation are best seen in the enlarged section of the ring as shown inFIG. 2. The central opening 21 of the ring is aligned with and open tothe primary lumen 15 of the catheter shaft. The outer wall 22 of thering contains the apertures 23 which form the jets, ejecting fluidradially outward. The sleeve 13 which fits over the ring and thecatheter shaft (FIG. 1) contains further apertures 25 which are alignedwith the apertures 23 in the ring when the parts are assembled. In theembodiment shown in these drawings, the ring apertures 23 are four innumber, as are the sleeve apertures 25, one corresponding to each of thesecondary lumens. Also in this embodiment, the ring apertures 23 arerectangular slits which open on one face of the ring (in this case thedistal face 27).

One closure 28 is associated with each ring aperture, and as shown inFIG. 2, the closures are separated by partitions 29. Each closure isformed as a lever 30 with a fulcrum 31 at one end and a stopper 32 atthe other. Pivoting of the lever occurs about a pivot axis which passesthrough the fulcrum 31 in the direction perpendicular to the plane ofthe Figure and thereby parallel to the longitudinal axis of thecatheter. The stopper 32 is aligned with the ring aperture 23 and isshaped to seal off the aperture when lowered into it. Attached to thelever at a location between its two ends is a hook 33 which is receivedin a recess 34 within which the hook travels back and forth inapproximately the radial direction of the ring as the lever pivots. Inits raised position (the position shown in the drawing), the hook 33engages a complementary hook 35 which extends inward from the outer wall22 of the ring and serves as a stop for the range of motion of themobile hook 33. The complementary contacting surfaces of these hooksalso serve as a seal against the passage of fluid when the hooks areengaged.

The portion of the lever extending from the fulcrum 31 to the hook 33together with the facing portion of the outer wail 22 of the ring forman enclosure 36. When the parts are assembled, the enclosure 36 isenclosed at its proximal end by the distal end 14 of the catheter shaft11 (see FIG. 1), and at its distal end by a shoulder 37 at the distalend of the sleeve. Each of these enclosures 36 is in axial alignmentwith one of the secondary lumens 16, whose opening is shown in dashedoutline in FIG. 2. When the pressure in the secondary lumen 16 exceedsthe pressure in the primary lumen 21 to cause a pressure differentialacross the lever 30, the enclosure expands until the hooks 33, 35engage, and the lever is pushed outward toward the center of the ring.This movement of the lever in turn unseats the stopper 32 from theaperture 23. When the pressure in the secondary lumen is released, thelever returns to its original position, reseating the stopper againstthe aperture. The direction of motion of the lever and hence the stopperis indicated by the arrows 39, 40.

Return of the stopper to the seated position against the aperture may beachieved by a reverse pressure differential created by lowering thepressure in the secondary lumen below that in the primary lumen.Alternatively, the material of construction of the lever 30 and/or itsshape and that of the fulcrum may be selected or designed to cause thelever to return to the closed position upon the relaxation of forces incontact with it. The stopper would thus automatically reseat uponrelaxation of the pressure in the secondary lumen. The ability to reseatindependently may be enhanced if the contacting hooks 33, 35 permit aslow leakage of the pressurization fluid past them, thereby releasingthe pressure in the enclosure 36 when the supply pressure is removed.

When the stopper 31 is seated against the aperture in this example, theseating is enhanced by angled lateral surfaces 38 on the stopper. Theseangled surfaces amplify changes in the width of the opening relative tothe lowering or raising of the stopper.

The closures 28 shown in FIGS. 1 and 2 thus act in response to pressuresignals transmitted through the secondary lumens 16, the pressuresignals being periods of high or low pressures relative to the pressureof the jet fluid in the primary lumen 15, the periods being ofcontrolled duration. A high pressure in one secondary lumen will unseatthe stopper 32 and turn on the associated jet, whereas a low pressurewill close the stopper and turn off the jet. The independenttransmission of these pressure signals permits independent operation ofthe closures, and jets are emitted selectively as desired to achieve thedirectional steering of the catheter tip by reaction force.

In the embodiment shown in FIG. 2, the lever 30 and the connectingfulcrum 31 where the lever is joined to the outer wall 22 of the ting ispreferably constructed and shaped such that the stopper 32 is seated inthe aperture 23 in the absence of a pressure differential. This is a"normally-closed" closure. For normally-closed closures in general,positive pressure signals are needed to activated the respective jets.As an alternative to the structure shown in FIGS. 1 and 2, the fulcrumof the closure (and hence its point of attachment to the ting 22) may besituated in the center of the lever, with the enclosure 36 on one sideand the stopper 32 on the other. A positive pressure in the secondarylumen 16 will then close the stopper rather than open it, and theclosure will be "normally-open" rather than "normally-closed."

Further alternatives are those in which the lever 30 is positionedfurther toward the outer wall 22 of the ting, placing the enclosure 36between the secondary lumen 16 and the outer wall 22. This will requirean additional partition along the inside rim of the ring to complete theenclosure. Here as well, the fulcrum will either be at the center of thelever or at one end. Alternatives to the use of a lever, although stilloperating in response to pressure signals transmitted along the lengthof the catheter, may also be devised. The stopper may for example be aninflatable bladder positioned to close the aperture only when inflated.Still further constructions and arrangements utilizing the underlyingconcepts of this invention will be apparent to those skilled in the art.

The ring 12 with its lateral apertures and closures can be manufacturedin a variety of ways. Micromachining methods such as those used in thefabrication of semiconductor chips are particularly useful. Examplesare:

(1) Laser micromachining of a blank disk to form the various openingsand contours by etching or ablation;

(2) Thick film deposition, i.e., the deposition of multiple layers ofparticles on a substrate through a mask, using the process of physicalvapor deposition, followed by removal of the layers from the substrateand the mask;

(3) Chemical vapor deposition over a substrate, again through a mask;

(4) Ion vapor deposition, again through a mask; and

(5) Metal plating, using selective buildup methods. A variety ofsubstrates may be used for the deposition and plating procedures. Apreferred substrate is silicon.

In certain embodiments of the invention, the catheter containsfunctional elements either for the transmission of diagnostics andsensor signals from the distal end to the proximal end of the catheter,or for performing a therapeutic function at the distal end, or both. Thefunctional element may be mounted on an axial shaft 41 as shown in FIG.3, passing through the primary lumen 15, or it may itself be a separatelumen 42 as shown in FIG. 4, either coaxial with or offset from theprimary lumen 15. For signal transmitting purposes, the functionalelement may be a radiopaque marker, a fluoroscopic contrast agentretained in a reservoir such as a microballoon, an optical fiber, or anultrasonic transducer. For therapeutic purposes, the functional elementmay be a cutting blade, an abrading element such as a grinding burr, alaser ablation element, an angioplasty balloon or simply a lumen fordelivering a therapeutic fluid which may be either a drug or an abradingsolution or slurry. Other possibilities will be readily apparent tothose skilled in the art.

FIGS. 5 and 6 represent an embodiment of the invention which is similarin certain ways to the embodiment shown in FIGS. 1 and 2, but differs inthe direction of rotation of the strip containing the lever and closure.

The catheter 51 has a central passage or primary lumen 52 enclosed atthe distal end by a ring 53. Each jet is formed by a pair of radiallyaligned apertures 54, 55 on either side of a chamber 56 formed withinthe wall of the ring 53. Inside the chamber is a lever arm 57 adjoinedto the internal walls of the chamber by pivot posts 58, 59, which permitrotation of the lever arm about an axis directed radially relative tothe catheter.

As shown in FIG. 6, the lever arm pivots between two positions, oneshown in solid lines in which one end 60 of the lever arm (the stopperend) lies between the two apertures 54, 55 and thereby shuts off the jetemerging through those apertures, and the other shown in dashed lines inwhich the stopper end 60 is clear of the two apertures, causing the jetto flow outward from the primary lumen 52. The range of movement of thelever arm 57 is restricted by blocking posts 61, 62. The position of thelever arm is governed by pressurized fluid fed to the chamber 56 ateither side of the pivot axis by lumens 63, 64. By using separatesupplies of pressurized fluid for each side of the lever arm, thisconstruction does not rely on the pressure in the primary lumen 52 tomaintain the arm in any one position. The individual supplies may beregulated such that the apertures are either normally-open ornormally-closed.

FIG. 7 illustrates an embodiment which does not utilize levers, butinstead utilizes axially movable rods or pistons 71. The pistons residein lumens 72 in which they are sufficiently loose to permit them to moveback and forth axially. They may be forced forward by fluid pressure inthe lumens or by electromagnetic means such as by the use of coils 73serving as miniature solenoid valves. Alternatively, the coils may beused to retract the pistons until fluid pressure forces them forward. InFIG. 7, the lowermost piston is shown in an extended position while theremaining three pistons are in a retracted position.

When in the extended position, the pistons 71 cover apertures 74 in thedistal ring 75 of the catheter. Stops 76 at the distal terminus of thering limit the range of motion of the pistons and retain them in thecatheter. Pistons which are retracted are clear of the apertures,thereby permitting jets to emerge through those apertures.

A system for operating a steerable catheter in accordance with thisinvention and for supplying all necessary fluids is shown in FIG. 8. Thecatheter 81 has distal 82 and proximal 83 ends, and contains foursecondary lumens, thereby supplying four jets 84. Although foursecondary lumens are included in this drawing, this number is used forillustrative purposes only. The actual number may be other than four,depending on the type of closure and its operation, as well as thenumber of jets, as explained above.

Four supply conduits 85 are connected to the proximal end of thecatheter, one such conduit feeding each of the four secondary lumens.Pressurized gas or liquid for use in these conduits originates from acommon source 86, which may be a reservoir with a downstream pump, apressurized container, or any other means of supply appropriate for thedesired pressure. The pressurized gas or liquid passes through a safetyregulator 87 which protects the system from overpressurized fluid. Fromthe regulator, the fluid passes through a manifold 88, then to a seriesof four valves 89 arranged in series, one of these valves per supplyconduit 85.

The valves are individually controlled by control signals from acomputer 91 of conventional programming for catheter operation. Thevalves 89 are normally open in this particular embodiment, and closeupon receiving pulse-modulated signals from the computer. Referring tothe embodiment of FIGS. 1 and 2 as an example, closure of any singlevalve results in opening of the corresponding jet closure 28 at thedistal end of the catheter, and ejection of fluid from the jet.

The fluid for the jets themselves is supplied by a separate fluid source92, which again may be a reservoir with a downstream pump, a pressurizedcontainer, or any other means of supply appropriate for the desiredpressure. For this source as well, a safety regulator 93 protects thesystem from overpressurization.

The four valves 89 may be solenoid valves, pressure-operated valves orany other type of valve controllable by control signals from a computer.The valves preferably have a high frequency response to cause them toopen and close rapidly in response to the control signals.

In one application of the system shown in FIG. 8, the computer 91 emitscontrol signals to the valves 89 based on information from a sensoraffixed to the catheter 81 near its distal end. The sensor may be anultrasonic transducer, an optical fiber, or any other of the variety ofknown means for collecting information at the distal end of the catheterand transmitting it to the proximal end. The information from the sensoris transmitted backward through the catheter through an imaging system94 and from there to the computer 91. When the catheter is positioned ina blood vessel, for example, signals from the sensor are processed bythe imaging system 94 to generate a virtual map, or two-dimensional orthree-dimensional image of the interior of the vessel and the positionof the catheter inside the vessel. The information produced by theimaging system may for example be a tabulation of distances from thecatheter to the vessel wall as a function of radial angle.Alternatively, the information may be a video image of the vesselsurrounding the catheter.

The information generated by the imaging system 94 can be used by theoperator to direct the catheter tip along a desired path through manualoperator input. To accomplish this, the operator uses a manual controldevice 95 such as a joystick, a mouse, a touch-sensitive display panel,or any other known type of directional control device. Signals from thecontrol device 95 will be transmitted to the computer which will thencalculate the appropriate sequence of control pulses and transmit themto the valves 89 according to the calculated sequence.

This is but one of a variety of ways in which a computer system such asthat shown in FIG. 8 can be used. The system may also be used to directthe catheter along a predetermined path, with the computer programmedaccordingly prior to the insertion of the catheter. A further use wouldbe to integrate the system with therapeutic action such as cutting,abrasion or ablation. For this use, the therapeutic element will beincorporated into the catheter construction as described above andfunctioning of the element will be controlled by an external controlunit 96. The physician will designate undesirable tissue or the presenceof an undesired deposit on an image generated by the imaging system. Thecomputer is then programmed to generate a series of cutting or ablationpaths until the specified tissue or deposit is destroyed or removed.

The foregoing is offered primarily for purposes of illustration. It willbe readily apparent to those skilled in the art that the components ofthe system, their configuration, arrangement and operation can befurther modified or substituted in various ways without departing fromthe spirit and scope of the invention.

What is claimed is:
 1. A steerable catheter, comprising:an elongatecatheter body having proximal and distal ends, a longitudinal axis and acylindrical side wall; a lumen extending the length of said catheterbody; at least one radial port at the distal end of said catheter bodyin said catheter body in said cylindrical side wall, said radial portcommunicating said lumen with the exterior of said catheter body; atleast one closure mounted to said catheter body at said distal end, saidclosure positioned to engage said radial port, said closure constructedto be driven by a signal selected from the group consisting of a fluidpressure signal and an electrical signal, said signal transmitted alongthe length of said catheter body from said proximal end; and signaltransmission means for transmitting signals capable of driving saidclosure to said closure from said proximal end of said catheter body toeffect opening and closing of said radial port.
 2. A steerable catheterin accordance with claim 1 in which said lumen is defined as a primarylumen, said closure is constructed to be driven by a fluid pressuresignal, and said signal transmission means comprises a secondary lumencommunicating fluid pressure from said proximal end of said catheterbody to said closure.
 3. A steerable catheter in accordance with claim 1in which said closure is constructed to be driven by an electricalsignal, and said signal transmission means comprises an electricalconduit extending the length of said catheter body.
 4. A steerablecatheter in accordance with claim 2 in which said signal transmissionmeans further comprises:a source of pressurized fluid; and a valveexternal to said steerable catheter, joining the proximal end of saidsecondary lumen to said source of pressurized fluid.
 5. A steerablecatheter in accordance with claim 1 in which said lumen is defined as aprimary lumen, said closure comprises a stopper affixed to lever meanspivotally mounted to said catheter body, and said signal transmissionmeans comprises a secondary lumen communicating fluid pressure to saidlever means.
 6. A steerable catheter in accordance with claim 5 furthercomprising a flexible linkage joining said closure pivotally to saidcatheter body, said linkage serving as a fulcrum for said lever means.7. A steerable catheter in accordance with claim 5 in which said levermeans is mounted to said catheter body for pivoting about an axisparallel to said longitudinal axis of said catheter body.
 8. A steerablecatheter in accordance with claim 5 in which said lever means is mountedto said catheter body for pivoting about an axis which is radialrelative to said catheter body.
 9. A steerable catheter in accordancewith claim 1 in which said closure comprises a piston movable parallelto said longitudinal axis, between a first position in which a lateralsurface of said piston closes said radial port, and a second position inwhich said piston clears said radial port, and said signal transmissionmeans comprises means for communicating an electrical signal to governthe position of said piston.
 10. A steerable catheter in accordance withclaim 1 in which said closure comprises a piston movable parallel tosaid longitudinal axis, between a first position in which a lateralsurface of said piston closes said radial port, and a second position inwhich said piston clears said radial port, and said signal transmissionmeans comprises fluid pressure transmission means for communicatingfluid pressure to drive said piston.
 11. A steerable catheter inaccordance with claim 1 comprising a plurality of said radial portsdistributed around the circumference of said cylindrical side wall, anda plurality of said closures, one such closure positioned to engage eachof said radial ports, and said signal transmission means is means forcommunicating signals independently to each of said closures.
 12. Asteerable catheter in accordance with claim 11 in which said lumen isdefined as a primary lumen, and said signal transmission means comprisesa plurality of secondary lumens, at least one such secondary lumencommunicating said proximal end of said catheter body to each of saidclosures.
 13. A steerable catheter in accordance with claim 12 in whichsaid primary lumen is coaxial with said catheter body, and saidsecondary lumens are distributed around the periphery of said primarylumen.
 14. A steerable catheter in accordance with claim 12 in whichsaid signal transmission means is pressure communication means furthercomprising:a source of pressurized fluid; and a plurality of valvesexternal to said steerable catheter, one of said valves joining theproximal end of each of said secondary lumens to said source ofpressurized fluid.
 15. A steerable catheter in accordance with claim 12in which each said closure comprises a stopper affixed to lever meanspivotally mounted to said catheter body; and in which at least one suchsecondary lumen communicates fluid pressure to each said lever means.16. A steerable catheter in accordance with claim 15 further comprisinga plurality of flexible linkages, one such flexible linkage joining eachsaid closure pivotally to said catheter body, and each said linkageseparating the stopper from the lever means of said closure.
 17. Asteerable catheter in accordance with claim 11 in which said lumen isdefined as a primary lumen, and said fluid pressure communication meanscomprises a plurality of secondary lumens, at least one such secondarylumen communicating said proximal end of said catheter body to each ofsaid closures, and in which said lever means form movable boundarysegments between said primary lumen and said secondary lumens at saiddistal end of said catheter body.
 18. A steerable catheter in accordancewith claim 11 in which said plurality of radial ports comprises from 3to 12 radial ports distributed around the circumference of said catheterbody at said distal end at substantially regular intervals.
 19. Asteerable catheter in accordance with claim 11 in which said pluralityof radial ports comprises from 4 to 8 radial ports distributed aroundthe circumference of said catheter body at said distal end atsubstantially regular intervals.
 20. A steerable catheter in accordancewith claim 11 in which said closures are normally closed, such that saidclosures close said radial ports in the absence of a signal beingtransmitted through said signal transmission means.
 21. A steerablecatheter in accordance with claim 11 in which said closures are normallyclosed, such that said closures maintain said radial ports closed in theabsence of a signal being transmitted through said signal transmissionmeans.
 22. A steerable catheter in accordance with claim 1 in which saidsignal is defined as a closure-driving signal, and said steerablecatheter further comprises an element transmitting a detectable signal,said element affixed to said distal end to permit monitoring of thelocation of said distal end.
 23. A steerable catheter in accordance withclaim 22 in which said element further permits imaging of tissuesurrounding the location of said distal end.
 24. A steerable catheter inaccordance with claim 22 in which said signal transmitting element is amember selected from the group consisting of a radiopaque marker, afluoroscopic contrast agent, a tip of an optical fiber, an ultrasonictransducer, and an element emitting electrical energy for etching orablation.
 25. A steerable catheter in accordance with claim 1 furthercomprising a therapeutic element affixed to said distal end.
 26. Asteerable catheter in accordance with claim 25 in which said therapeuticelement is a member selected from the group consisting of a cuttingelement, an abrading element, a laser ablation element and anangioplasty balloon.
 27. A steerable catheter in accordance with claim 1further comprising a therapeutic fluid supply lumen for supplying atherapeutic fluid to said distal end of said catheter.